ArratList 重写toString 如何实现

List list = new ArrayList(); list.add(12); System.out.println(list);//输出 [12]

如上，我们都知道，List、Set 继承了Collection集合，输出[12],是因为重写了toString，

但是toStringn你知道是具体在那实现的吗？

让我们先来看一下他们的继承结构：

原来是在AbstractCollection类中重写了toString方法，源码如下：

/** * Returns a string representation of this collection. The string * representation consists of a list of the collection's elements in the * order they are returned by its iterator, enclosed in square brackets * (<tt>"[]"</tt>). Adjacent elements are separated by the characters * <tt>", "</tt> (comma and space). Elements are converted to strings as * by {@link String#valueOf(Object)}. * * @return a string representation of this collection */ public String toString() { Iterator<E> it = iterator(); if (! it.hasNext()) return "[]"; StringBuilder sb = new StringBuilder(); sb.append('['); for (;;) { E e = it.next(); sb.append(e == this ? "(this Collection)" : e); if (! it.hasNext()) return sb.append(']').toString(); sb.append(',').append(' '); } }